Creep and recovery behavior of selectively degraded sealants

The time‐dependent structure development of sealants changes drastically when subjecting the materials to selective degradation. By passing sealants through a Graco pump several times, the rheological properties affecting end use performance change appreciably. After only two passes in the pump the sealant is no longer classified as a ‘‘usable’’ product. This selective degradation lowers viscosity (lesser effect), elasticity, and yield stress, all due to a change in the structure of the material. The viscoelasticity of the sealant compounds was studied using a Rheometrics Controlled Stress Rheometer. By monitoring the creep and elastic recovery of the selectively degraded compounds, a correlation was developed between performance properties (end use applications) and time‐dependent structure formation. Creep and recovery results indicate that the sealants behave as viscoelastic materials. Results obtained at low stresses show elastic deformation and high viscosity. At higher stresses structural breakdown occurs resulting in lower viscosity with little or no elasticity. After two passes through the Graco pump the sealant drastically loses structure properties related to the end use performance. Viscosity, elasticity, and yield stress are lowered due to a breakdown in the time‐dependent structure development. The recoverable strain, which relates directly to elasticity, decreases appreciably with increasing passes. The degradation of the sealant changes the structure development which relates directly to the viscoelastic properties.